One-component development is performed by pressing a supply roller etc. against a developing roller to supply a toner on the developing roller, making the toner to be electrostatically held on the developing roller, forming the toner into a thin layer with a regulating blade, friction-charging the toner, and supplying the toner to a photoconductor to develop with the toner. One-component development can realize downsize in weight and cost saving compared to two-component development or magnetic one-component development.
Moreover, sizes of particles of a toner obtained by pulverization have been reduced in order to improve image quality and therefore there is a need for homogeneously disperse a colorant, a charge-controlling agent, or a release agent in a thermoplastic resin. When dispersion is insufficient, the colorant, charge-controlling agent, or release agent added to the toner comes at an outer surface of the toner particle in the process of pulverization. As a result, irregular-shape toner particles having a low average circularity are generated in a very fine powder region having particle diameters of 3 micrometers or smaller. When toner particles are observed per single particle, moreover, there are problems, such as variations in amounts of raw materials contained in the toner particle, and an increase in an amount of the raw materials exposing to a surface of the toner particle. Accordingly, toner-charging failures occur due to unevenness of the toner particles, and problems, such as conveying failures and deterioration in image quality due to background smear, occur.
In order to solve the above-described problems, proposed are to regulate a ratio of toner particles having the low average circularity or an abundance ratio of toner particles having different circularity to a certain range, to control an abundance of very fine powder region (3 micrometers or smaller) to a certain value or lower, and to control shapes of toner particles in the very fine powder region.
For example, PTL 1 (Japanese Unexamined Patent Application Publication No.
2009-25749) discloses a toner for the purpose of providing a toner having excellent flowability and capable of forming a high quality image of high definition and high resolution, a production method of the toner, a two-component developer, a developing device, and an image forming apparatus. The toner includes at least a binder resin and a colorant. The toner includes a particle group of a large particle diameter and a particle group of a small particle diameter. A volume average particle diameter of the small particle diameter-particle group is smaller than a volume average particle diameter of the large particle diameter-particle group. A volume average particle diameter D50V a cumulative volume of which from the large particle diameter side in a cumulative volume distribution is 50% is 4 micrometers or greater but 8 micrometers or smaller. An amount of toner particles having a volume average particle diameter of 7 micrometers or greater is 24% by volume or greater but 47% by volume or less. An amount of toner particles having a number average particle diameter of 5 micrometers or less is 10% by number or greater but 50% by number or less.
Moreover, PTL 2 (Japanese Unexamined Patent Application Publication No. 2006-139051) discloses a toner used for a two-component developer including a silicone-coated carrier and the toner for the purpose of providing an excellent electrostatic latent image-developing toner and two-component developer where a charge-controlling agent is securely fixed on surfaces of particles of the toner even when the low-fixing toner is used, fogging caused particularly by a difference in a charge amount between the toner in the developer and the supply toner is prevented, and deterioration of the developer is prevented. The toner includes toner base particles each including at least a binder resin, a colorant, and a release agent, a charge-controlling agent, and inorganic particles. When the toner is supplied, an average circularity of the toner measured by a flow particle image analyzer is 0.930 through 0.965 and an amount of fine particles of 3 micrometers or smaller is 5% by number through 20% by number. After the toner is supplied, an amount of fine particles of 3 micrometers or smaller in the toner in a developing device is 5% by number through 70% by number.